This invention relates generally to shear cut systems for cutting webs of paper-like material, and, more particularly, to a blade mounting arrangement for such systems.
The existing technology for cut-off systems for cutting webs of paper-like material is well known. Representative perforation cut-off systems are shown in U.S. Pat. Nos. 2,478,240 and 3,247,747, for example. One characteristic of these prior art cut-off systems is the required close tolerance in the setting of the cutting blades to each other.
Very high stresses occur between the cut-off blade and the blade holder. This high stress concentration can cause blade cracking or fatigue failure. Moreover, because there is no damper in the system, the lower stiffness of the system is provided by the blade itself. Therefore, the cut-off blade will vibrate to release the dynamic energy due to the action of impact forces, which can result in miss-off.
The interference between the cutting blades is normally in the range of 0.004 to 0.010 inch. When the interference between the cutting blades is below 0.004 inch, cutting performance is jeopardized. When the interference between the cutting blades is above 0.010 inch, the cutting forces are high, the stress concentrations in the cutting blades are high which cause premature fatigue failure, and the higher forces cause vibrations. Vibrations can cause a change in the interference which causes cut-off performance reliability problems. As the cutting system (i.e., the web being cut) becomes wider, the close tolerance requirements cause problems.
There have been efforts to reduce the vibrations in the cutoff blades. Examples of systems designed to reduce vibrations are shown in U.S. Pat. Nos. 3,733,949 and 5,125,302. These patents disclose blade mounting arrangements which incorporate an elastomeric material in contact with the cut-off blade. The elastomeric material comprises a thin, flat pad that is generally rectangular in shape. Although this configuration provides for vibration damping, such configuration also establishes a specific relationship for cutting force, blade cutting interference, blade stress level and stress concentration.
In the blade mounting structure disclosed in U.S. Pat. No. 3,733,949, for example, the pad is sized to occupy most of the depth of the recess in which the cut-off blade is mounted, and leaves only a slight spacing or gap between the pad and the cut-off blade. Also, the planar pad extends generally coextensive with the free portion of the blade. These factors limit the ability to make adjustments for the stiffness of the system. Moreover, although this blade mounting arrangement reduces noise, it does not allow large interference between blades because it increases the stiffness of the whole system. Consequently, this mounting arrangement can cause premature failure of the blade if the interference between blades is not set up absolutely correctly. In addition, this known blade mounting arrangement does not allow the load to be controlled in accordance with the allowable deflection at the blade tip.
It is an object of the present invention to provide a blade assembly for a shear cut roll for perforating or cutting sheet material.
It is a further object of the present invention to provide an improved blade mounting arrangement for a cut-off blade of a shear cut type, cut-off system.
It is another object of the present invention to provide a blade mounting arrangement which reduces stress concentration between a cut-off blade and a blade holder of a shear cut type, cut-off system.
A further object of the invention is to maintain flexibility of a cut-off blade of a shear cut type, cut-off system.
Another object of the invention is to increase impact strength in a shear cut type, cut-off system.
Yet another object of the invention is reduce vibration and noise in a shear cut type, cut-off system.